You can’t judge a book by its cover, nor can you judge a shoe by its color. Look below the surface and you’ll find a variety of materials, which leads to debate over which is best. Discover the parts of your shoes and the materials manufacturers use to make them.
Parts of a Shoe
The Upper – This is the material that covers the top of the foot. While this provides the style of the shoe, it does not contribute to the cushioning of the shoe. Uppers are made from leather, satin, suede, canvas, and hybrid materials.
The Outsole – This is the part of the shoe that comes in direct contact with the ground. This is where the cushioning of your foot begins. Outsoles are made of PU or polyurethane, rubber, TPR (which is the combination of PU and rubber), leather, plastic, and rubber sheets.
The Insole – This is the part of the shoe that comes in contact with the bottom of your foot. It provides much of the cushioning of the shoe and often is removable to accommodate orthotics. Insoles can be made of materials like cowhide, silicone, cotton, or foam.
The Mid-Sole – This layer is sandwiched between the insole and the outsole. This is the part of the shoe that provides most of the shock absorption. It is often made of multiple materials to provide the best combination of support and flexibility. Although some shoes may not have a mid-sole, most shoes designed for comfort and shock absorption will have a midsole. The most common midsole material is EVA, which is a combination of two plastics. Polyurethane is not used as often at EVA because it’s heavier and less flexible. Thermal plastic is used to prevent over-pronation.
The Heel – Not surprisingly this is the portion of the shoe that absorbs the shock from when your heel strikes the ground. Depending on the shoe, heels are usually made of synthetics or leather combinations.
Common Shoe Materials
Ignoring proprietary materials that some shoe companies have, the two most popular materials are polyurethane and EVA. These are foams with millions of tiny air bubbles that provide the basis of the cushion. By changing the amount of air bubbles in the foam the designer can create the desired combination of cushioning, shock absorption, and durability.
Polyurethane – This is a type of dense foam that provides a great deal of cushioning and shock absorption for a longer period of time. Because it is so dense it can feel heavier, seem stiffer, and may not feel quite as cushioned as shoes that use EVA. It is most commonly used in walking shoes because it provides a great deal of stability and comfort.
The outsole and heel of shoes are often made of this material because of its resiliency. Polyurethane is able to provide all-over cushioning and shock absorption as well as stability in areas that need a little more support.
EVA (Ethylene vinyl acetate) – This is a lighter density foam that is quite popular in running shoes because of the cushioning and flexibility that it provides. When it is used as dense foam it can be used as a part of the outsole but it is most frequently used as lighter foam in the mid-sole of shoes
Many products use different types of EVA to provide a combination of support and cushioning in different parts of the foot. A dual-density EVA mid-sole is made when two types of EVA are combined in the same mid-sole. Using a combination can provide support for the arch while giving a great deal of cushioning on the outside of your foot.
Another common product used in the outsole is rubber. This material provides a great deal of traction as well as some shock absorption. There are a variety of rubber materials companies use to manufacture shoes including thermo-plastics and latex.
Shoe materials are often used in combination with each other in the same part of the shoe. A mid-sole may be comprised of both EVA and polyurethane. Or rubber may be added to a polyurethane outsole to increase the traction in areas like the front of the foot and the heel.
If you suffer from bunions or other foot ailments, be sure to ask your podiatrist which materials he or she recommends for your particular ailment.